23,171 research outputs found
Environmental Effects of Space Shuttle Solid Rocket Motor Exhaust Plumes
The deposition of NOx and HCl in the stratosphere from the space shuttle solid rocket motors (SRM) and exhaust plume is discussed. A detailed comparison between stratospheric deposition rates using the baseline SRM propellant and an alternate propellant, which replaces ammonium perchlorate by ammonium nitrate, shows the total NOx deposition rate to be approximately the same for each propellant. For both propellants the ratio of the deposition rates of NOx to total chlorine-containing species is negligibly small. Rocket exhaust ground cloud transport processes in the troposphere are also examined. A brief critique of the multilayer diffusion models (presently used for predicting pollutant deposition in the troposphere) is presented, and some detailed cloud rise calculations are compared with data for Titan 3C launches. The results show that, when launch time meteorological data are used as input, the model can reasonably predict measured cloud stabilization heights
Light-cone Quantum Mechanics of the Eleven-dimensional Superparticle
The linearized interactions of eleven-dimensional supergravity are obtained
in a manifestly supersymmetric light-cone gauge formalism. These vertices are
used to calculate certain one-loop processes involving external gravitini,
antisymmetric three-form potentials and gravitons, thereby determining some
protected terms in the effective action of M-theory compactified on a
two-torus.Comment: 31 pages, harvmac (b); A minor TeX error correcte
NO sub X Deposited in the Stratosphere by the Space Shuttle Solid Rocket Motors
The possible effects of the interaction of the plumes from the two solid rocket motors (SRM) from the space shuttles and mixing of the rocket exhaust products and ambient air in the base recirculation region on the total nitrous oxide deposition rate in the stratosphere were investigated. It was shown that these phenomena will not influence the total NOx deposition rate. It was also shown that uncertainties in the particle size of Al2O3, size distributions and particle/gas drag and heat transfer coefficients will not have a significant effect on the predicted NOx deposition rate. The final results show that the total mass flow of NOx leaving the plume at 30 km altitude is 4000 g./sec with a possible error factor of 3. For a vehicle velocity of 1140 meter/sec this yields an NOx deposition rate of about 3.5 g./meter. The corresponding HCl deposition rate at this altitude is about a factor of 500 greater than this value
Cosmological perturbations in a gravity with quadratic order curvature couplings
We present a set of equations describing the evolution of the scalar-type
cosmological perturbation in a gravity with general quadratic order curvature
coupling terms. Equations are presented in a gauge ready form, thus are ready
to implement various temporal gauge conditions depending on the problems. The
Ricci-curvature square term leads to a fourth-order differential equation for
describing the spacetime fluctuations in a spatially homogeneous and isotropic
cosmological background.Comment: 5 pages, no figure, To appear in Phys. Rev.
Conserved cosmological structures in the one-loop superstring effective action
A generic form of low-energy effective action of superstring theories with
one-loop quantum correction is well known. Based on this action we derive the
complete perturbation equations and general analytic solutions in the
cosmological spacetime. Using the solutions we identify conserved quantities
characterizing the perturbations: the amplitude of gravitational wave and the
perturbed three-space curvature in the uniform-field gauge both in the
large-scale limit, and the angular-momentum of rotational perturbation are
conserved independently of changing gravity sector. Implications for
calculating perturbation spectra generated in the inflation era based on the
string action are presented.Comment: 5 pages, no figure, To appear in Phys. Rev.
The Origin of Structures in Generalized Gravity
In a class of generalized gravity theories with general couplings between the
scalar field and the scalar curvature in the Lagrangian, we can describe the
quantum generation and the classical evolution of both the scalar and tensor
structures in a simple and unified manner. An accelerated expansion phase based
on the generalized gravity in the early universe drives microscopic quantum
fluctuations inside a causal domain to expand into macroscopic ripples in the
spacetime metric on scales larger than the local horizon. Following their
generation from quantum fluctuations, the ripples in the metric spend a long
period outside the causal domain. During this phase their evolution is
characterized by their conserved amplitudes. The evolution of these
fluctuations may lead to the observed large scale structures of the universe
and anisotropies in the cosmic microwave background radiation.Comment: 5 pages, latex, no figur
Relativistic Hydrodynamic Cosmological Perturbations
Relativistic cosmological perturbation analyses can be made based on several
different fundamental gauge conditions. In the pressureless limit the variables
in certain gauge conditions show the correct Newtonian behaviors. Considering
the general curvature () and the cosmological constant () in the
background medium, the perturbed density in the comoving gauge, and the
perturbed velocity and the perturbed potential in the zero-shear gauge show the
same behavior as the Newtonian ones in general scales. In the first part, we
elaborate these Newtonian correspondences. In the second part, using the
identified gauge-invariant variables with correct Newtonian correspondences, we
present the relativistic results with general pressures in the background and
perturbation. We present the general super-sound-horizon scale solutions of the
above mentioned variables valid for general , , and generally
evolving equation of state. We show that, for vanishing , the
super-sound-horizon scale evolution is characterised by a conserved variable
which is the perturbed three-space curvature in the comoving gauge. We also
present equations for the multi-component hydrodynamic situation and for the
rotation and gravitational wave.Comment: 16 pages, no figure, To appear in Gen. Rel. Gra
Electron-boson spectral density of LiFeAs obtained from optical data
We analyze existing optical data in the superconducting state of LiFeAs at 4 K, to recover its electron-boson spectral density. A maximum entropy
technique is employed to extract the spectral density from
the optical scattering rate. Care is taken to properly account for elastic
impurity scattering which can importantly affect the optics in an -wave
superconductor, but does not eliminate the boson structure. We find a robust
peak in centered about 8.0 meV or 5.3 (with 17.6 K). Its position in energy agrees well with a similar
structure seen in scanning tunneling spectroscopy (STS). There is also a peak
in the inelastic neutron scattering (INS) data at this same energy. This peak
is found to persist in the normal state at 23 K. There is evidence that
the superconducting gap is anisotropic as was also found in low temperature
angular resolved photoemission (ARPES) data.Comment: 17 pages, 6 figure
Anisotropic strains and magnetoresistance of La_{0.7}Ca_{0.3}MnO_{3}
Thin films of perovskite manganite La_{0.7}Ca_{0.3}MnO_{3} were grown
epitaxially on SrTiO_3(100), MgO(100) and LaAlO_3(100) substrates by the pulsed
laser deposition method. Microscopic structures of these thin film samples as
well as a bulk sample were fully determined by x-ray diffraction measurements.
The unit cells of the three films have different shapes, i.e., contracted
tetragonal, cubic, and elongated tetragonal for SrTiO_3, MgO, and LaAlO_3
cases, respectively, while the unit cell of the bulk is cubic. It is found that
the samples with cubic unit cell show smaller peak magnetoresistance than the
noncubic ones do. The present result demonstrates that the magnetoresistance of
La_{0.7}Ca_{0.3}MnO_{3} can be controlled by lattice distortion via externally
imposed strains.Comment: Revtex, 10 pages, 2 figure
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